Original ALS: 4 ohms nominal; dipped to @1 ohm at certain frequencies; very difficult amp load, least efficient of the ALS designs, 4x12" woofers (honeycomb type), 4x30" ribbons. There was a Platinum upgrade available that changed out the 4x30" ribbons for 2x60" ribbons & swapped out the crossover. I believe the upgrade changed the nominal impedance to >6 ohms.

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